Measurement of local retinal ganglion cell layer thickness in patients with glaucoma using frequency-domain optical coherence tomography

Abstract

Objective: To explore the feasibility of obtaining a local measurement of the thickness of the retinal ganglion cell layer in patients with glaucoma using frequency-domain optical coherence tomography (fdOCT) and a computer-aided manual segmentation procedure.

Methods: The fdOCT scans were obtained from the horizontal midline for 1 eye of 26 patients with glaucoma and 20 control subjects. The thickness of various layers was measured with a manual segmentation procedure aided by a computer program. The patients were divided into low- and high-sensitivity groups based on their foveal sensitivity on standard automated perimetry.

Results: The RGC plus inner plexiform and the retinal nerve fiber layers of the low-sensitivity group were significantly thinner than those of the high-sensitivity group. While these layers were thinner in the patients than the controls, the thicknesses of inner nuclear layer and receptor layer were similar in all 3 groups. Further, the thinning of the retinal ganglion cell plus inner plexiform layer in 1 glaucoma-affected eye showed qualitative correspondence to the loss in 10-2 visual field sensitivity.

Conclusions: Local measures of RGC layer thickness can be obtained from fdOCT scans using a manual segmentation procedure, and these measures show qualitative agreement with visual field sensitivity.

Figures

Figure 1

The frequency-domain optical coherence tomographic scan location and segmentation technique. A, The location of the 6×6–mm (gray) scan volume and the single horizontal line scan (green) are superimposed on a fundus image. B, A horizontal line scan of one of the controls shows the 5 borders determined as part of the computer-aided segmentation technique. They are (1) red, the border between the vitreous and the retinal nerve fiber layer (RNFL); (2) orange, the border between the RNFL and the retinal ganglion cell layer (RGC); (3) green, the border between the inner plexiform layer (IPL) and the inner nuclear layer (INL); (4) light blue, the border between the INL and outer plexiform layer (OPL); and (5) violet, the border between the Bruch membrane (BM) and the choroid. REC+ indicates receptor and OPL layers. C, A horizontal line scan of a patient with glaucoma shows loss of the RNFL and RGC layer.

Figure 2

The thickness profiles for individual controls (colored curves) for the retinal nerve fiber layer (A), retinal ganglion cell + inner plexiform layer (B), inner nuclear layer (C), and receptor+outer plexiform layer (D). The mean limits (2 SD) are indicated by the bold black curves.

Figure 3

The thickness profiles for individual patients (colored curves) for the retinal nerve fiber layer (A), retinal ganglion cell + inner plexiform layer (B), inner nuclear layer (C), and receptor+outer plexiform layer (D). The mean limits (2 SD) for the controls from Figure 2 are indicated by the bold black curves.

Figure 4

The mean thickness profiles (1 SE) for the controls, patients with high central sensitivity, and patients with low sensitivity for the retinal nerve fiber layer (A), retinal ganglion cell+ inner plexiform layer (B), inner nuclear layer (C), and receptor+outer plexiform layer (D).

Figure 5

The 10-2 total deviation of visual field (center) of the left eye of a patient with glaucoma. The scan images (left and right) are from the 6×6–mm volume scan and correspond to the horizontal lines of the test points in the 10-2, as shown by the black lines. The segmentation borders of the retinal ganglion cell + inner plexiform layer (RGC+) are shown by orange and green curves. The thickness of the RGC+ layer (distance between the orange and green borders) is shown as red curves in the accompanying graph, with the thickness from a single control of a similar age shown in blue.